What You Don't Know About Airplane Oxygen Masks

You’ve eyed that little compartment above your seat on the plane where the ever elusive oxygen mask lives, but odds are, you won't ever have to use one. "Federal Aviation Administration research shows that supplemental oxygen has been needed roughly 2,800 times over a 40-year period [on U.S. airlines]," FAA Spokesperson Allen Kenitzer tells Condé Nast Traveler. "The frequency of occurrences necessitating the use of oxygen is approximately ten events per one billion flight hours."

The oxygen masks deploy automatically when there is a loss of cabin pressure. This could happen for any number of reasons, including a tear in the fuselage or anything that causes the pressurization system—or the valves that continually pump air into the aircraft to mimic the breathable concentrations of oxygen at lower altitudes—to malfunction. Still, in most cases, aircraft design (and crew training) mean these incidents are survivable if the masks deploy as they should.

The air above 10,000 feet has too few oxygen molecules per particle of air for humans (and other animals) to breathe, and that’s where the pressurization system comes in; essentially recreating what it feels like to breathe at five to eight thousand feet. When that pressurization system fails, the masks automatically deploy, and you have just seconds—on average, 18—to get the mask on before you start to feel the effects of a lack of oxygen. Without oxygen, you will quickly feel drowsy and even euphoric, a phenomenon known as hypoxia, but as time passes, continued lack of oxygen to the brain will lead to blackouts, passing out, and possibly even death.

When the pressure drops in the cabin, oxygen masks will fall. Once you affix the mask to your face, you can breathe normally and a continuous supply of air begins to flow. The bag doesn't inflate but rises and falls with breathing, so no need to panic if it seems like it's not working—it is.

There isn’t actually any oxygen in the oxygen masks. Instead, there are several chemicals that, when combined, mimic breathable oxygen (including obscure-sounding compounds like barium peroxide and sodium chlorate, among others). Airlines opt for this compound over plain old oxygen tanks to minimize the combustible elements on board your flight. If the chemicals sound potentially hazardous to humans, that’s because they quite possibly are— though experts say not putting on the mask is more dangerous than the dust particles you might inhale from the chemicals. You’ll smell something burning when the masks deploy, as the chemicals combine to form the new substance. The masks won’t deploy in the event of an actual fire, as the chemicals could fuel the flames.

Once you’ve secured the mask, there’s anywhere from ten to 20 minutes’ worth of life-preserving oxygen in them. In most models, the masks won't stop the flow of air until the chemicals are all used up. That’s generally more than enough time for the pilot to get the plane down to an altitude where you can breathe without aid, though you should always follow your pilot and flight attendants' instructions before removing the mask.